In a manufacturing facility, a product usually has to be processed at many work stations or processing machines. The transporting or conveying of partially finished products, or work-in-process parts, is an important link in the total manufacturing process. The conveying process is especially important in the manufacturing of integrated circuit products. In fabricating an IC product, a multiplicity of fabrication steps, i.e., as many as several hundred, are usually required to complete the fabrication of an IC circuit. A semiconductor wafer or an IC chip must be transported between various fabrication stations for conducting various processes.
For instance, to complete the fabrication of an IC circuit, various steps of deposition, cleaning, ion implantation, etching and passivation steps must be completed before an IC chip can be packaged for shipment. Each of these fabrication steps must be performed in a different process machine, such as a chemical vapor deposition chamber, or an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer therefore must be conveyed between various work stations many times before it is completed. The conveying and the tracking of such WIP parts in a semiconductor fabrication plant therefore becomes a very important link in the total fabrication process.
Conventionally, partially finished semiconductor wafers or IC chips are conveyed in a fabrication plant by automated vehicles traveling on tracks or by manually operated push carts. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes and then placed in a container commonly known as a pod. The cassette of wafers can be loaded into a pod from the bottom of the pod since the top is sealed off to reduce the possibility of contamination. The pod that contains semiconductor wafers is then transported on a vehicle either in an automated fashion or in a manually operated fashion.
In a conventional method, the vehicles are equipped with shelves and guard rails surrounding the shelves for placement of containers or pods. For identifying and locating the various WIP parts contained in the pods, the pods are labeled with a tag positioned on the side of the pod. The tags can be read automatically by a tag reader that is normally mounted on the guard rails of the vehicle. Each tag reader has an output cable for outputting the data it reads. In a typical factory set-up, certain areas of the factory are designated as depots for stowing the vehicles and the containers it carries. At these designated areas, electrical receptacles are provided in the floor such that the output cable from each tag reader can be plugged in. For a typical manually operated push cart, six pods for carrying semiconductor wafers are normally loaded onto three separate shelves. Six separate output cables from the tag readers must then be plugged into six different electrical receptacles mounted in the floor in order to input data into a computer system for monitoring the whereabouts of the WIP parts. In operation, when an operator manually pushes a cart (or a cart may be moved automatically on a track) to the depot area, the operator must manually plug in the output cables six times in order to register the locations of the WIP parts carried on the cart. This becomes a very labor intensive process and thus not a desirable method of monitoring the WIP parts in a factory.
It is therefore an object of the present invention to provide a mobile work-in-process parts tracking system that does not have the drawbacks or shortcomings of the conventional system.
It is another object of the present invention to provide a mobile work-in-process parts tracking system that is capable of tracking a vehicle carrying a plurality of containers of WIP parts.
It is a further object of the present invention to provide a mobile work-in-process parts tracking system that is capable of tracking a plurality of parts containers that it carries by connecting a single cable to a data concentrator mounted in the factory floor.
It is another further object of the present invention to provide a mobile work-in-process part tracking system that utilizes a data concentrator for providing a common wire for ground and power supply to all the tag readers that it receives data from.
It is yet another object of the present invention to provide a work-in-process parts tracking system by using a data concentrator such that a single cable can be used to output all data received into the concentrator by plugging into a data distributor mounted in the factory floor.
It is still another object of the present invention to provide a work-in-process parts tracking system by utilizing a data concentrator which is mounted on the vehicle and outputting data from a single cable into a distributor which is mounted in the factory floor.
It is still another further object of the present invention to provide a method of tracking work-in-process parts in a manufacturing plant by transporting the parts on a vehicle and then reading data from the parts containers into a data concentrator such that a single cable output from the concentrator can be plugged into a data distributor located in the factory floor for monitoring the whereabouts of the WIP parts.